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Basic Research—TechnologyMicro–Computed Tomography Study of the Internal Anatomyof Mesial Root Canals of Mandibular MolarsMarcelo Haas Villas-B^as, DDS, Norberti Bernardineli, DDS, PhD, oBruno Cavalini Cavenago, DDS, Marina Marciano, DDS, Aldo del Carpio-Perochena, DDS,Ivaldo Gomes de Moraes, DDS, PhD, Marco H. Duarte, DDS, PhD, Clovis M. Bramante, DDS, PhD,and Ronald Ordinola-Zapata, DDS, MScAbstractIntroduction: The aim of this study was to determine Key Wordsthe mesiodistal and buccolingual diameter, apical Dental anatomy, mandibular molars, micro–computed tomographyvolume, and the presence of isthmuses at the apicallevel of mesial root canals of mandibular molars.Methods: Sixty extracted ﬁrst and second mandibularmolars were scanned by using a SkyScan 1076 micro– K nowledge of the dimensional variations of complex root canal systems such as those in mesial roots of mandibular molars is indispensable to support clinical decisions during endodontic procedures. Anatomical knowledge includes distinguishing thecomputed tomography system with a voxel size of 18 presence of isthmuses during surgical or nonsurgical treatment (1, 2) and anmm. The apical thirds of the samples were reconstructed appropriate determination of the apical anatomical diameter (3). These anatomicalto allow a perpendicular section of the apical third by variables cannot be determined in the typical radiographic exam taken before treatmentusing the multiplanar reconstruction tool of the OsiriX and can compromise the cleaning and shaping procedure of endodontic treatment,software. The mesiodistal and the buccolingual which decreases the success rate because of the infectious characteristics of apical pe-distances of root canals were measured between the riodontitis.1- to 4-mm levels. The type of root canal isthmuses Previous studies have described the apical diameter of internal anatomy of severalpresent at these levels was classiﬁed by using modiﬁed groups of teeth (3–5). Adequate apical diameter determination is only reliable if thecriteria of Hsu and Kim. The volume of the root canal cross sections are taken perpendicular to the long axis of the root canal (6). However,anatomy between the 1- to 3-mm apical levels was ob- the determination of the apical diameter in curved root canals such as mesial roottained by using the CTAN-CTVOL software. Results: The canals of mandibular molars can be difﬁcult with this method. At least 3 limitationsmedians of the mesiodistal diameter at the 1-, 2-, 3-, to performing adequate cross sections are identiﬁed. (1) The root canal foramen isand 4-mm levels in the mesiobuccal and mesiolingual not always present at the anatomical root apex (7, 8); consequently, the root canalcanals were 0.22 and 0.23 mm, 0.27 and 0.27 mm, curvature in the last apical millimeter does not always resemble the trajectory of the0.30 and 0.30 mm, and 0.36 and 0.35 mm, respectively. external anatomy. (2) Mandibular molars present multiplanar curvatures in 100% ofThe buccolingual lengths at the 1-, 2-, 3-, and 4-mm cases in both mesiodistal and buccolingual directions (9). (3) The main apical foramenlevels were 0.37–0.35 mm, 0.55–0.41 mm, 0.54–0.49 of the buccal and lingual canals can be present at different levels, which makes it difﬁcultmm, and 0.54 and 0.60 mm, respectively. The presence to ﬁnd an exact section at the same level for both canals. In addition, the presence ofof isthmuses was more prevalent at the 3- to 4-mm isthmuses is not uncommon (10), and these data have not been reported in previouslevel. However, 27 cases presented complete or incom- studies that addressed the canal diameter determination (4). The concept of enlargingplete isthmuses at the 1-mm apical level. The mean of the root canal by using 3 larger ﬁles to eliminate the infected dentin at the total circum-the volume of the apical third was 0.83 mm3, with ference might not be applicable when an isthmus is present. Consequently, it is not cleara minimum value of 0.02 and a maximum value of 2.4 what percentage of root canal walls of mandibular molars can be appropriatelymm3. Conclusions: Mesial root canals of mandibular enlarged by mechanical means, especially at the apical third.molars do not present a consistent pattern. A high vari- Micro–computed tomography (micro-CT) is a nondestructive technology that isability of apical diameters exists. The presence of isth- useful to evaluate the apical diameter of mandibular molars in which 2 canals aremuses at the apical third was not uncommon even at present, because the sections can be nondestructively reoriented in several ways tothe 1-mm apical level. (J Endod 2011;37:1682–1686) gain a perpendicular section for each canal in both planes. In addition, the apical volume of the root canals including ﬁns and isthmuses can be properly quantiﬁed by using dedicated software (11), and the results can be compared with the volume of endodontic instruments (12). From the Department of Endodontics, Bauru Dental School, University of S~o Paulo, Bauru, S~o Paulo, Brazil. a a Supported by the Brazilian Funding Agencies CNPq (grant 134981-2009) and FAPESP (grant 2010/16002-4). Address requests for reprints to Dr Ronald Ordinola-Zapata, Faculdade de Odontologia de Bauru, USP, Al. Octvio Pinheiro Brisolla, 9-75, 17012-901 Bauru, aS~o Paulo, Brazil. E-mail address: ronaldordinola@usp.br a0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists.doi:10.1016/j.joen.2011.08.0011682 Villas-B^as et al. o JOE — Volume 37, Number 12, December 2011

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Basic Research—Technology Apical volume and percentage of untreated surfaces after rotary ‘‘stack’’ was exported as TIFF ﬁles and then imported to the OsiriX soft-instrumentation are variables that have been extensively studied by ware (http://www.osirix-viewer.com). This software has been usedusing micro-CT technology in maxillary molars (13). However, the previously for measurements of micro-CT data of hominin fossil teethapical volume in mandibular molars before instrumentation proce- (20). Appropriate calibration of the voxel size was performed to allowdures has not been extensively studied except for 2 previous studies posterior measurements. Then the apical thirds of the samples were re-that reported the total volume of this root canal system (14, 15). constructed to allow a perpendicular section of each mesial root canal Accuracy of micro-CT linear and volumetric measurements on ex- at the 1- to 4-mm apical third levels according to Weiger et al (6). Fortracted teeth has been previously reported (16–18). Therefore, a more this purpose the multiplanar reconstruction tool of the OsiriX softwarereliable determination of the apical diameter could be expected in was used. The mesiodistal and buccolingual distances of the mesialcomparison to previous studies that used horizontal cross sections. canals were calculated by using the measurement tool of the OsiriX soft-To date, there is no report addressing the apical diameter of ware, and the results were expressed in micrometers. Buccolingualmandibular molars by using micro-CT. The aim of this study was to distances were measured when an isthmus was not present or whendetermine the mesiodistal and buccolingual diameter, apical volume, an incomplete isthmus did not cross the middle line of the root. Toand the presence of isthmuses at the apical level of mesial root canals conﬁrm the accuracy of the measurements, an object with a knownof mandibular molars. geometry (ProTaper F2 instrument; Dentsply-Maillefer, Baillagues, Switzerland) was scanned by using the described protocol. The instru- ment was sectioned at the 21-mm level by using an IsoMet (Buehler, Materials and Methods Lake Bluff, IL) saw machine, and the expected diameter of the instru- Sixty extracted ﬁrst and second mandibular molars with curva- ment (1.2 mm) was veriﬁed by using a stereomicroscope (Stemitures between 20 and 35 and 19- to 21-mm length were selected 2000C; Carl Zeiss, Jena, Germany) and the Axiovision software (Carl(19). The teeth were extracted for extensive caries or coronal fractures, Zeiss) at 40Â; the measurement was compared with the micro-CT valueand ethical requirements for the use of extracted teeth were followed found by using the OsiriX software.(CEP 131-2010). After extraction, the teeth were immediately stored The type of root canal isthmus present at the 1- to 4-mm levels wasin 10% formalin solution. classiﬁed by 2 independent evaluators by using the criteria of Hsu and The samples were scanned by using a micro-CT system (Skyscan Kim (21). In Type I, there are 2 or 3 canals with no notable communi-1076, Kontich, Belgium) with a voxel size of 18 mm. The complete cation. In Type II, there are 2 canals with a connection between the 2Figure 1. (A) Mesiodistal diameter distribution of values found at 1- to 4-mm apical levels. (B) Buccolingual diameter distribution of values found at 1- to 4-mmapical levels. The median and 25th–75th percentile of canal diameters are also shown. (C) Distribution of apical volumes found between the 1- and 3-mm levels in60 samples. Values are expressed in mm3. The median and 25th–75th percentile are also shown. (D) Distribution of isthmuses found at 1- to 4-mm apical levels inthe categories studied. MB, mesiobuccal; ML, mesiolingual; SM, single mesial canal.JOE — Volume 37, Number 12, December 2011 Micro-CT Study of Internal Anatomy of Mesial Root Canals of Mandibular Molars 1683

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Basic Research—Technologymain canals. Type III differs from Type II because of the presence of 3 was 0.83 mm3. Representative pictures of the internal anatomy of repre-canals instead of 2 canals. In Type IV, canals extend to the isthmus area. sentative samples are shown in Figure 2.Type V is deﬁned as a true connection or corridor throughout thesection. Incomplete isthmuses were classiﬁed as Type Ia. The apical Discussionvolume between the 1- to 3-mm apical levels was determined by using The study of the dimensions of the internal anatomy of teeth hasthe CTAN-CTVOL software, and the data were expressed in mm3. Eval- been a challenge since the studies of Kuttler (22) and Kerekes and Tro-uations were made using descriptive statistics. Isthmus data were stand (4). Although conventional radiographs used during clinicalanalyzed by the c2 test at a conﬁdence level of P < .05. procedures can show important details such as the number of root canals, the severity of the root canal curvature, or the presence of calci- Results ﬁcations, periapical x-rays are bidimensional images and do not No differences were found for the stereomicroscope and micro-CT provide enough details of the internal anatomy. For this reason anatom-measurements of the evaluated endodontic instrument. ical studies are necessary to guide clinicians to achieve better cleaning The presence of complete (Types II–V) and incomplete isthmuses of the root canals.(Ia) was a common ﬁnding at all the evaluated levels in 20 and 7 cases at Previous studies (1, 10) and a recent systematic review (23)the 1-mm level, 28 and 5 cases at the 2-mm level, 36 and 7 cases at the 3- showed a high incidence of isthmuses in mandibular molars betweenmm level, and 37 and 4 cases at the 4-mm level, respectively, but the pres- the 2-mm and 4-mm levels. Those data are in agreement with the resultsence was statistically signiﬁcant at the 3- and 4-mm levels in comparison of this study. However, an important point not fully addressed by previousto the 1-mm level (Fig. 1) (P < .05). For the buccolingual diameter deter- studies addressing the apical diameter determination is that whenmination, 3 incomplete isthmuses were found across the middle line of a complete or incomplete isthmus is present, it is impossible to determinethe mesial root at the 1-mm level, 3 at the 2-mm level, 6 at the 3-mm level, an exact buccolingual diameter. The aim of manual or rotary instrumen-and 3 at the 4-mm level. These cases and types II–V isthmuses were tation is to enlarge the apical third for an appropriate irrigation to ensureexcluded for the determination of the buccolingual diameter. Buccolin- the placement of medicaments and ﬁnally to facilitate ﬁlling proceduresgual diameter determination was possible in 37, 29, 18, and 20 cases at (24). It was found that in 23 cases the apical diameter could not be deter-the 1-, 2-, 3-, and 4-mm levels, respectively. The medians, 25th–75th mined at the 1-mm apical level because of the presence of complete orpercentiles, and distribution of the values corresponding to the mesiodis- incomplete isthmuses. Previous studies have shown that buccal andtal and buccolingual diameters are presented in Figure 1. lingual areas of ﬂattened root canals with or without isthmus cannot The median of apical volume was 0.72 mm3, with a range of 0.03– be completely reached by rotary instruments or ﬁlled appropriately (2,2.41mm3. The 25th–75th percentile was 0.48–1.08 mm3, and the mean 25–27). Histologic and micro-CT studies have also found it difﬁcult toFigure 2. Tridimensional reconstructions and micro-CT sections of the studied samples at the 1- to 3-mm levels (bar represents 1 mm). The volume of intereststudied between 1- to 2-mm and 2- to 3-mm levels is represented by different colors (A–D). A great variability of the internal root canal anatomy is observed.1684 Villas-B^as et al. o JOE — Volume 37, Number 12, December 2011